Wish
DX  » Community » Forums
«See all threads (in Electronics)
Electronics

DIY laptop powerbank project

  • sheepish Top 10 Forum Poster Thursday, March 2, 2017 6:40 PM Reply

    However, I'm trying to think of a way to [utilise] the buzzer's
    electricity to trigger a relay that switches off all the 4 balance-wire
    relays...


    That sounds clever. Do you know about using two relays to latch each other on?

    Remembering 30 years.
    Posts(24946) | Reviews | Tip post

  • Ignatus Thursday, March 2, 2017 8:14 PM Reply

    Hi sheepish,


    Thanks for pointing me in the right direction!


    I've vaguely heard about latching relays in the past, but generally this new territory for me.


    I found a nice resource and will try to wrap my mind around it and a suitable solution asap.


    http://www.the12volt.com/relays/page5.asp#mtc


    -Seems like it is within my two lone grey cell's capacity to figure it out ;)



    Greetings.


    Posts(190) | Reviews | Tip post

  • Ignatus Thursday, March 2, 2017 8:54 PM Reply

    On another note, I'm still considering to upgrade this battery to a 6s6p configuration.


    I own SKU: 433805 which can balance charge only up to a 4s battery. Could I use two of these chargers simultaneously on the 6s battery in a 2x3s or 1x4s+1x2s balance charging configuration?


    -Or would they interfere with each other?




    Posts(190) | Reviews | Tip post

  • sheepish Top 10 Forum Poster Friday, March 3, 2017 4:28 AM Reply

    Why not split the battery completely in two so you actually have two separate 3s batteries?

    Remembering 30 years.
    Posts(24946) | Reviews | Tip post

  • Ignatus Friday, March 3, 2017 5:22 AM Reply

    Because the voltage of a 3S battery @11.11V nominal  is too low to operate the 15V and/or
    20V laptop without being constantly boosted, losing precious amps
    in the process.


    I don't know what the formular is to follow for voltage step-up coversions, but I know it is inefficient compared to a step-down converter.


    Let's assume a 11.11V nominal 3s6p battery with 20Ah capacity needs to be constantly boosted to 20V. I guess we'd lose at least 50% of the capacity when boosting  to 20V during the process = 10Ah ?



    Anyhow, the latching relays idea brings up many more mindboogling posssibilities!


    How about creating two seperate 3s batteries built into one single enclosure, each having their own 3s protection board and two Lipo chargers built in.


    When the batteries are in use they are switched to a 6s configuration and the moment they are being re-charged they become two independent 3s batteries that get balance charged by two seperate Lipo chargers.



    Posts(190) | Reviews | Tip post

    post edited by Ignatus on 3/3/2017 at 5:24 AM
  • sheepish Top 10 Forum Poster Friday, March 3, 2017 5:29 AM Reply

    I wasn't suggesting you should use them as 3S batteries. At the risk of more nostalgia, have you ever used a 2xAA or 2xD incandescent torch? In each case you just put two separate units into the torch in series.

    Remembering 30 years.
    Posts(24946) | Reviews | Tip post

  • Ignatus Friday, March 3, 2017 1:51 PM Reply

    Hi Sheepish, sorry for the delayed reply. -  I was swamped with other, more urgent tasks.

    Yes, I thought you were heading in that direction with the 2x3s idea.

    Nostalgia alert:

    Disassembling and modding flashlights was my favorite hobby as a boy. I actually took any toy apart that had lights or motors in them to build something new, or just see how they work. When I was 6 years old my first soldering iron was a candle, because my parents wouldn’t buy me the real thing and I had to urgently fix a loose wire on my remote controlled porsche :)

    And, yes!  - I remember all too well the happiness I felt when stacking multiple D sized cells in series to watch the bulb shine brighter and brighter until it blew.


    Back on topic:

    I just checked again for the 6s BMS (from another source) and it is also just a protection board without charging capabilities. That means I’d need to buy a large Lipo charger that can handle 6s balance charging, if I were to build a single 6s battery.

    Your 2x3s split battery idea is very neat, but I would want automation.

    That means it should be a 6s battery during operation, all in a single enclosure. Then when power comes in from a solar panel or by other means, it splits automatically into two 3s batteries, which get charged by two inbuilt 3s Lipo chargers.

    I haven’t had the time yet to figure out in detail a circuit based on multiple relays that can accomplish that.

    Off the top of my head, the "2x3s  automated 6s battery" would require:

    1 SPST relay  as master on/off for output
    6 SPST relays for the balance leads
    5 SPDT relays to control 2Lipo chargers - Latched on/off via momentary pulse from one of the Lipo chargers' alarm buzzers

    I have to make a guess without having put any deeper thought into this, additionally required are maybe:

    8 SPDT relays to switch the state of the battery between 6s to 2x3s and vice versa when external power comes into the Lipo chargers to start the charging process.

    = possibly somewhere around 20 relays.

    Sounds like good fun designing that circuit! - Apart from the fact that 20 regular sized relays would take up an inappropriate amount of space.

    This micro SPDT relay SKU: 289783 is unfortunately sold out at the moment. I only have one unit here and it’s just rated for 12V, but I may need a few 24V rated ones for parts of that circuit.

    Right now, I also own only one spare 3s battery protection board and one Lipo charger.

    Sooner or later, I'll start to look around and order parts for the upcoming fun & advanced 2x3s battery project, but decided that I stick with the 4s battery design for now.


    -Gain some experience and mayb!e soon get some satisfaction from having accomplished building one usable unit.

    5 new micro SPST relays for the 4s balance leads cut-off feature will arrive tomorrow and I still have to test the Lipo alarm/buzzer operating actions. Then see if I can come up with a latching relays solution to kill off the Lipo charger, which hopefully can be accomplished with the parts that I already own.


    The rotary switch and breakout board mentioned in the first post, which is supposed to replace the trimmer will reach here sometime during next week. - I just placed the order yesterday.


    Thanks for all your feedback and ideas Sheepish, it is highly appreciated!

    -It helps me think through various possible solutions.




    Edit: Typos

    Posts(190) | Reviews | Tip post

    post edited by Ignatus on 3/3/2017 at 5:12 PM
  • Ignatus Tuesday, March 7, 2017 8:35 PM Reply

    Hello again dear DX community :)



    Battery run-time

    Over the last few days I’ve tested the DIY battery for real-world usage.

    I’ve recharged the laptop’s internal battery, which is rated at 4615mAh, via the 4s6p (<<<edit fixed typo), 20Ah DIY battery while the laptop was in use/switched on.

    Three times from 0% to 100% and I’ve also used the laptop while it's internal batteries were at 100%, additionally for approx. 7 hours in total.  -The results are very decent.



    Battery protection board

    I’m not entirely happy with the battery protection board SKU: 255209

    When I drained the DIY battery, the protection board did allow one cell-pack to discharge way down to 2.9V before shutting down the entire battery’s output.

    Also, I find the holes in the solder pads too small to put some thick wires through it. For just a few Amps it is okay, but if one  plans on pulling more than 4-5A ...


    - It is pretty difficult to connect some thick wires through/to it. Furthermore, 2 of the solder pads are far too closely positioned to some smd fuses.




    Reset BMS


    Another issue with this protection board is that if you’ve drained the DIY battery down so far that it shuts off, then it will come back ON only after the cells have been recharged to around 4.1V !

    -The only way to partially re-charge the DIY battery and the start using it again is to RESET the BMS/ battery protection board.

    To reset it, one has to apply power to the "load" pads. One can either use an external supply, or alternatively - I’ve manually connected the battery’s own terminals to the “load" pads just for a fraction of second and then the BMS started to work again/was reset ,even though I was only 50% through the charge-cycle.

    -I will either have to either add a momentary switch into the box/enclosure or find another, more automated way for the BMS to reset, if I don’t want to always wait till the battery is 99% recharged.


    The only other alternative is buy a "real" Lipo charger that charges via XT60 connecters and does the balance charge via the balance wires.




    Charge time

    Currently, I’m charging with this balance-charger SKU: 433805, which is a bit too under-powered for a 4s6p 20Ah battery.

    I powered the lipo charger with a 12V 5A external power supply and it took almost exactly 17 hours to charge the battery back to 100% / 4.2V per cell-pack from approx. 2.9V

    -A bit too slow for my taste, although very gentle on the Lipos.



    Balance Charge wires auto connect/ disconnect feature

    I’ve completed today the auto cut-off / auto switch-on latching relay setup.


    confused_relay.png


    It is to ensure that the balance wires of the Lipo charger are disconnected when the Lipo charger’s buzzer makes a sound once charging is complete and it also ensures that the balance leads become only connected to the battery when the Lipo charger beeps one time as soon as power is supplied to it from the DC socket.



    However, the latching relay set-up is mightily confusing and I’m wondering if I got it right and I’m afraid to blow up my one and only Lipo charger.


    I hope Desolder or Sheepish, or somebody else knowledgeable could please confirm that I understand this schematic right? :

    latchonoffspnd.jpg


    a.) The little motor / load icon represents my Lipo charger’s buzzer?
    b.) The blue positive wire labeled as 12V Output is can be used to control another relay?
    c.) Why is the red positive labeled as “fused 12V constant”? What does it mean and where do I attach it to? -To the same 12V source/DC socket that powers the Lipo charger or to my DIY battery?



    Thanks,
    Ignatus

    Posts(190) | Reviews | Tip post

    post edited by Ignatus on 3/7/2017 at 8:49 PM
  • Ignatus Wednesday, March 8, 2017 5:09 AM Reply

    Update:


    It kind of works sometimes. I’ve created a few simple test setups (without the Lipo charger). When I really fast strike together the 2 wires that are on the load icon then this relay setup works as a latching relay most of the time. Important is that the connection is made and disconnected again extremely fast/ fraction of a second.

    Another issue is that it puts out 12V on the load icon related wires and I’m haven’t measured yet, but I highly doubt that the Lipo charger’s buzzer runs on 12V.

    I also read that many other people having issues with this particular latching relay setup and I’m not sure yet what the final solution will be.


    I read about (overpriced) Impulse relays, 555 circuits and I'm currently watching Youtube videos on Flip-Flop circuits.

    Posts(190) | Reviews | Tip post

  • sheepish Top 10 Forum Poster Thursday, March 9, 2017 5:47 PM Reply

    When I drained the DIY battery, the protection board did allow one
    cell-pack to discharge way down to 2.9V before shutting down the entire
    battery’s output.


    One of the Trustfire 2400 cells I tested discharged to 2.4 V. Most I stopped myself when they got to 2.55 V. 2.9 V sounds pretty good.


    That pic of the relays is awesome. I'm going to have to take more than a cursory glance at your schematic to figure out if it should work. Do you have fuses in appropriate places? Oh...


    a.) The little motor / load icon represents my Lipo charger’s buzzer?


    Or a momentary push button. Something's got to switch it, right?


    b.) The blue positive wire labeled as 12V Output is can be used to control another relay?


    It's the output of this glorious mess, allowing you to switch things on and off.


    c.) Why is the red positive labeled as “fused 12V constant”? What does
    it mean and where do I attach it to? -To the same 12V source/DC socket
    that powers the Lipo charger or to my DIY battery?


    That's the best place to put an inline fuse, where the power comes into this switching, um, thing. It attaches to whatever you want to power the thing when it's doing its switching.


    I saw a clever circuit on YouTube using three transistors to do (I think) the same thing. It used a capacitor to change the delay for how long the button could be pressed for.


    Edit - https://www.youtube.com/watch?v=Foc9R0dC2iI - found after I mentioned latching relays earlier in this thread then started browsing YouTube (as you do these days).

    Remembering 30 years.
    Posts(24946) | Reviews | Tip post

    post edited by sheepish on 3/9/2017 at 5:57 PM
Page 5 of 11
Go to Page:
«Reply to this thread (in Electronics)
Electronics

Reply

Subject:

* 50 characters max

Message:

Please note: HTML codes are not allowed anywhere on this page (otherwise you will see an error).

Please note that DealExtreme Forums are not a sales or product support board. While we do constantly participate in this forum, please contact us via support ticket for a guaranteed fast response. We make every effort to make the quickest replies.

DX Everywhere